You can imagine many features that could show a male has genes for greater survival, or a greater ability to reproduce. Evolutionary theory shows that in these cases, three types of genes will all increase in frequency together: genes for a male “indicator” trait reflecting that he has good genes, genes that make a female prefer that indicator trait, and of course the “good” genes whose presence is reflected by the indicator. This is a complex scenario, but most evolutionary biologists consider it the best explanation for elaborate male traits and behaviors.
